Graphene has attracted much interest due to the possibility of graphene-based devices that may have better performance, such as speed and power consumption, than their semiconductor counterparts. This is expected because of the unique properties of graphene such as the high mobility of carriers, which gives high current densities. Moreover, graphene is expected to be suitable for spintronics due to the long spin relaxation lengths and the weak spin-orbit interaction. Graphene nanoribbons (GNRs) with designed edges offer methods to manipulate spin-polarized electrons. Spin valves are the most popular device in spintronics. Graphene-based spin valves have been experimentally demonstrated.
A typical magnetic tunnel junction has a sandwich structure F/I/F, where F indicates a ferromagnet and I indicates an insulating barrier. Currently, the mainstream structure of the insulating barrier is a single insulator material. The structure above is called a single-barrier structure, and the tunnel magnetoresistance (TMR) ratio can reach about 102%. Recently, double-barrier structures (e.g. F/I/F/I/F or F/I/N/I/F, where N is a metal) were proposed. The TMR ratio of a double-barrier structure can reach about 103%. The barrier segment of a magnetic tunnel junction must be thin enough to allow the tunnel effect in quantum mechanics.
A magnetic tunnel junction is an important component when designing hard disk read heads and magnetic random access memories, while the TMR ratio is an important indicator to assess the magnetic tunnel junction. For example, a magnetic tunnel junction with a higher TMR ratio can enhance the sensitivity of the hard disk read head, and thereby enhance the capacity of the hard disk. Another example is the magnetic field sensor. At present, the most sensitive magnetic field sensor is the superconducting quantum interference device (SQUID). However, the SQUID must operate at very low temperatures, and thus liquid nitrogen is needed. Through improving the sensitivity of the MTJ, we have the opportunity to obtain a magnetic field sensor which is as sensitive as the SQUID and has the advantage of working at room temperature.
Another structure similar to the magnetic tunnel junction is the giant magnetoresistance (GMR) structure. The GMR structure does not have a barrier, and thus no tunnel effect is involved. The typical material of its middle layer is a conductor. The GMR structure has a similar indicator: the magnetoresistance ratio. The magnetoresistance ratio of a GMR structure can reach about 102%.
After the magnetic tunnel junction was invented in 1995, it has been an important issue to design a magnetic tunnel junction with a higher TMR ratio. The goal of the present invention is to provide a magnetic tunnel junction with high TMR ratio.
In order to overcome the drawbacks in the prior art, a graphene-based magnetic tunnel junction with segmented potentials is disclosed. The particular design in the present invention not only solves the problems described above, but is also easy to implement. Thus, the present invention has utility for the industry.